Variable displacement hydraulic pump with electromechanical actuator and method thereof

ABSTRACT

A pump, including: inlet port and outlet ports; a cylinder block including a piston disposed in a through-bore; a swash plate engaged with the piston; a drive shaft non-rotatably connected to the drive shaft, arranged to rotate the cylinder block to draw fluid through the inlet port into the through-bore and to expel the fluid from the through-bore and through the outlet port and including an axis of rotation; an axis transverse to the axis of rotation; and an actuator including a roller screw; a nut disposed about the roller screw and in threaded contact with the roller screw; an actuator pin; and an electric motor arranged to rotate the roller screw or the nut to axially displace the actuator pin to pivot the swash plate or the cylinder block about the axis and control an amount of the fluid expelled from the through-bore.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) of U.S.Provisional Application No. 62/380,769, filed Aug. 29, 2016, whichapplication is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to a variable displacement hydraulic pumpwith torque sensing and a method thereof, in particular, a variabledisplacement hydraulic pump using torque sensing to attain or maintain adesired flow rate correlated to a known torque level on a drive shaftfor the pump.

BACKGROUND

Known variable flow hydraulic pumps use an auxiliary hydraulic controlpiston or an electromechanical controller to control the flow rate forthe pump. Feedback for control of the piston is typically provided bydown-stream (of the pump outlet) measurements of pressure or flow.However, pressure in the control piston is affected by the overallpressure in the hydraulic system, for example to due to activation ofvarious hydraulic components. Changes in the overall pressure causedeviations in the position of the piston, which in turn affects the flowrate of the pump. The control piston can be made more precise by usingan electromechanical actuator, but the control loop still has errors andlag induced by the down-stream measurement of pressure or flow. Thus, itis difficult to quickly and accurately attain or maintain a desired flowrate for known variable flow hydraulic pumps.

SUMMARY

According to aspects illustrated herein, there is provided a variabledisplacement axial pump, including: an inlet port; an outlet port; acylinder block including a first piston disposed in a firstthrough-bore; a swash plate engaged with the first piston; a drive shaftnon-rotatably connected to the drive shaft, arranged to rotate thecylinder block to draw fluid through the inlet port into the firstthrough-bore and to expel the fluid from the first through-bore andthrough the outlet port, and including an axis of rotation; an axistransverse to the axis of rotation; and an actuator including a rollerscrew, a nut disposed about the roller screw and in threaded contactwith the roller screw, an actuator pin engaged with the roller screw,and an electric motor arranged to rotate the roller screw or the nut toaxially displace the actuator pin to pivot the swash plate about theaxis and control an amount of the fluid expelled from the firstthrough-bore or pivot the cylinder block about the axis and control anamount of the fluid expelled from the first through-bore.

According to aspects illustrated herein, there is provided a variabledisplacement hydraulic pump, including: an inlet port; an outlet port; acylinder block including a through-bore and a piston at least partiallydisposed in the through-bore; a drive shaft non-rotatably connected tothe drive shaft, arranged to rotate the cylinder block to displace thepiston to draw fluid through the inlet port into the through-bore andexpel the fluid from the through-bore and through the outlet port, andincluding an axis of rotation; an axis transverse to the axis ofrotation; an actuator including a roller screw, a nut disposed about andin contact with the roller screw, an actuator pin engaged with theroller screw and the swash plate and an electric motor arranged torotate the roller screw to axially displace the actuator pin to pivotthe swash plate about the axis and control an amount of the fluidexpelled from the through-bore or pivot the cylinder block about theaxis and control an amount of the fluid expelled from the through-bore.

According to aspects illustrated herein, there is provided a variabledisplacement hydraulic pump, including: an inlet port; an outlet port; acylinder block including a through-bore and a piston at least partiallydisposed in the through-bore; a drive shaft non-rotatably connected tothe drive shaft, arranged to rotate the cylinder block to displace thepiston to draw fluid through the inlet port into the through-bore andexpel the fluid from the through-bore and through the outlet port, andincluding an axis of rotation; an axis transverse to the axis ofrotation; an actuator including a roller screw, a nut disposed about andin contact with the roller screw, an actuator pin engaged with theroller screw and the swash plate and an electric motor arranged torotate the nut to axially displace the actuator pin to pivot the swashplate about the axis and control an amount of the fluid expelled fromthe through-bore or pivot the cylinder block about the axis and controlan amount of the fluid expelled from the through-bore.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments are disclosed, by way of example only, withreference to the accompanying schematic drawings in which correspondingreference symbols indicate corresponding parts, in which:

FIG. 1 is a cross-sectional view of an electromechanical actuator for avariable displacement pump with a driven nut;

FIG. 2 is a cross-sectional view of an electromechanical actuator for avariable displacement pump with a roller screw;

FIG. 3 is a schematic representation of a variable displacement pumpwith a pivotable swash plate and including the actuator of FIG. 1 or theactuator of FIG. 2;

FIG. 4 is a schematic representation of the variable displacement pumpof FIG. 3 with the swash plate pivoted;

FIG. 5 is a schematic representation of a variable displacementbent-axis pump including the actuator of FIG. 1 or the actuator of FIG.2; and,

FIG. 6 is a schematic representation of the variable displacementbent-axis pump of FIG. 5 with a cylinder block pivoted.

DETAILED DESCRIPTION

At the outset, it should be appreciated that like drawing numbers ondifferent drawing views identify identical, or functionally similar,structural elements of the disclosure. It is to be understood that thedisclosure as claimed is not limited to the disclosed aspects.

Furthermore, it is understood that this disclosure is not limited to theparticular methodology, materials and modifications described and assuch may, of course, vary. It is also understood that the terminologyused herein is for the purpose of describing particular aspects only,and is not intended to limit the scope of the present disclosure.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood to one of ordinary skill inthe art to which this disclosure belongs. It should be understood thatany methods, devices or materials similar or equivalent to thosedescribed herein can be used in the practice or testing of thedisclosure.

FIG. 1 is a cross-sectional view of electromechanical actuator 100 for avariable displacement pump, with a driven nut. Actuator 100 includeshousing 102, electric motor 104, roller screw 106, nut 108 and actuatorpin 110. Pin 110 is engaged with screw 106, for example is axially fixedto screw 106 such that pin 110 axially displaces with screw 106. In anexample embodiment, motor 104 includes stator 112 and rotor 114. Nut 108is disposed about screw 106 and is in threaded engagement with screw106. For example, nut 108 includes threads 116 in contact with threads118 of screw 106. In an example embodiment, screw 106 is a differentialroller screw.

Electric motor 104 rotates nut 108 about axis of rotation AR1 for nut108 in opposite circumferential directions CD1 and CD2. In the exampleof FIG. 1, nut 108 is axially fixed and rotating nut 108 about axis ofrotation AR1 in opposite circumferential directions CD1 and CD2displaces screw 106 and pin 110 in opposite axial directions AD1 andAD2, respectively. In an example embodiment, rotating nut 108 about axisof rotation AR1 in opposite circumferential directions CD1 and CD2displaces screw 106 and pin 110 in axial directions AD2 and AD1,respectively. The discussion that follows is directed to rotation of nut108 about axis of rotation AR1 in circumferential directions CD1 and CD2displacing screw 106 and pin 110 in axial directions AD1 and AD2,respectively. However, it should be understood that the discuss thatfollows is applicable to rotation of nut 108 about axis of rotation AR1in circumferential directions CD1 and CD2 displacing screw 106 and pin110 in axial directions AD2 and AD1, respectively.

In an example embodiment, pump 100 includes resilient element 120.Element 120 reacts against housing 102 to urge screw 106 in directionAD2 to prevent back-driving of screw 106 in direction AD2. Thus, pump100 is self-locking. For example, when motor 104 is de-energized,element 120 frictionally engages threads 116 and 118 to prevent screw106 from rotating in direction CD2 and displacing in direction AD2.Element 120 can be any resilient element known in the art, including butnot limited to a wrap spring (shown in FIG. 1) or a spring-pressurizedfriction pad. In an example embodiment (not shown), pump 100 includes anelectromechanical brake to prevent back-driving of screw 106.

FIG. 2 is a cross-sectional view of electromechanical actuator 200 for avariable displacement pump, with a driven nut. Actuator 200 includeshousing 202, electric motor 204, roller screw 206, nut 208 and actuatorpin 210. Pin 210 is engaged with screw 206, for example is axially fixedto screw 206 such that pin 210 axially displaces with screw 206. In theexample of FIG. 2, screw 206 is an actuating pin as further describedbelow. In an example embodiment, motor 204 includes stator 212 and rotor214. Nut 208 is disposed about screw 206 and is in threaded engagementwith screw 206. For example, nut 208 includes threads 216 in contactwith threads 218 of screw 206. In an example embodiment, screw 206 is adifferential roller screw.

Electric motor 204 rotates screw 206 about axis of rotation AR2 forscrew 206 in opposite circumferential directions CD1 and CD2. In theexample of FIG. 2, nut 208 is rotationally fixed and rotating screw 206about axis of rotation AR2 in opposite circumferential directions CD1and CD2 displaces screw 206 and pin 210 in opposite axial directions AD1and AD2, respectively. In an example embodiment, nut 208 is rotationallyfixed and rotating screw 206 about axis of rotation AR1 in oppositecircumferential directions CD1 and CD2 displaces screw 206 and pin 210in axial directions AD2 and AD1, respectively. The discussion thatfollows is directed to rotation of screw 206 about axis of rotation AR1in circumferential directions CD1 and CD2 displacing screw 206 and pin210 in axial directions AD1 and AD2, respectively. However, it should beunderstood that the discuss that follows is applicable to rotation ofscrew 206 about axis of rotation AR2 in circumferential directions CD1and CD2 displacing screw 206 and pin 210 in axial directions AD2 andAD1, respectively.

FIG. 3 is a schematic representation of variable displacement pump 300with a pivotable swash plate and including actuator 100 of FIG. 1 oractuator 200 of FIG. 2. Pump 300 includes housing 302, inlet port 304,outlet port 306, drive shaft 308, cylinder block 310 non-rotatablyconnected to shaft 308, swash plate 312, actuator 100 or actuator 200,axis of rotation AR3 for shaft 308, and axis of rotation AR4 for block310. Cylinder block 310 includes through-bores 318 and 320 and pistons322 and 324 at least partially disposed in through-bores 318 and 320,respectively. The discussion that follows assumes actuator 100 isincluded in pump 300; however, it should be understood that thediscussion for actuator 100 in pump 300 is applicable to actuator 200 inpump 300.

By “non-rotatably connected” elements, we mean that: the elements areconnected so that whenever one of the elements rotates, all the elementsrotate; and relative rotation between the elements is not possible.Radial and/or axial movement of non-rotatably connected elements withrespect to each other is possible, but not required.

Pump 300 is located in device D (for example, a bulldozer, tractor, orconstruction equipment). Shaft 308 is rotated by engine E of device D.Actuator 100 is arranged to receive, from processor P, control signal328. Actuator 100 is arranged to: pivot swash plate 312 about axis A1,transverse to axis of rotation AR3, according control signal 328; ormaintain a circumferential position of swash plate 312, about axis AR3,according to control signal 328.

Pistons 322 and 324 are engaged with plate 312. Pistons 322 and 324remain engaged to plate 312 as is known in the art. In an exampleembodiment, each of pistons 322 and 324 is connected to swash plate 312via a respective retention assembly 330, as is known in the art. In anexample embodiment (not shown) fluids at ports 304 and 306 arepressurized to force pistons 322 and 324 into contact with plate 312during rotation of block 310 about axis AR3/AR4. For example, assemblies330 are not used to maintain connection between the pistons and plate312.

As cylinder block 310 rotates about axis AR3 and AR4: when piston 322 or324 is aligned with port 304, plate 312 has displaced piston 322 or 324in direction AD1, within through-bores 318 or 320, respectively, tocreate suction and draw fluid F into through-bore 318 or 320 throughport 304; and when piston 322 or 324 is aligned with port 306, plate 312has displaced piston 322 or 324 in direction AD2, within through-bores318 or 320, respectively, to expel fluid F from through-bore 318 or 320into port 306 at a flow rate. In FIG. 3, the flow rate is flow rate 332.

A flow rate at which fluid F is drawn into and expelled from pump 300 isdependent upon the speed of rotation of block 310 and the displacementof pistons 322 and 324, by plate 312, within through-bores 318 and 320,respectively. The speed of rotation of block 310 is a function of engineE, which is determined by operations other than those for pump 300. Thatis, the speed of rotation is not controllable by pump 300. For a givenposition of plate 312 about axis A1, increasing and decreasing the speedof rotation of block 310 increases and decreases rate 332, respectively.

A flow rate for pump 300 is also governed by the circumferentialposition of plate 312 with respect to axis A1. The circumferentialposition of plate 312 determines the distance that pistons 322 and 324are displaced by plate 312 within through-bores 318 and 320,respectively. In the example of FIG. 3, pistons 322 and 324 aredisplaced distance 334 by plate 312 within through-bores 318 and 320,respectively. Thus, pistons 322 and 324 displace distance 334 to drawfluid F into through-bores 318 and 320, respectively, and pistons 322and 324 displace distance 334 to expel fluid F from through-bores 318and 320, respectively.

As discussed below, changing the extent of the axial displacement ofpistons 322 and 324 (for example, distance 334) changes the amount offluid F drawn into and expelled by block 310 and hence changes flow rate332.

FIG. 4 shows variable displacement axial pump 300 of FIG. 3 with swashplate 312 pivoted. In the example of FIG. 4, swash plate 312 has beenrotated in direction CD3 about axis A1 from the position shown in FIG.3. The alignment of through-bores 318 and 320 with ports 304 and 306remains the same. The rotation and subsequent tilting of swash plate 312in FIG. 4 changes the axial displacement of pistons 322 and 322. As aresult: pistons 322 and 324 are displaced distance 336 by plate 312. Inthe example of FIGS. 3 and 4: distance 336 is less than distance 334.

Assuming a constant speed of rotation of shaft 308 in FIGS. 3 and 4, andsince distance 336 is less than distance 334, the amount of fluid Fdrawn into and expelled from through-bores 318 and 320 in FIG. 4decreases in comparison to the amount of fluid F drawn intothrough-bores 318 and 320 in FIG. 3. Thus flow rate 338 in FIG. 4 isless than rate 332 in FIG. 3.

The following discussion is directed to a transition from FIG. 4 to FIG.3. To transition from FIG. 4 to FIG. 3, swash plate 312 is pivoted byactuator 100 about axis A1 in direction CD4. Assuming a constant speedof rotation of shaft 308 in FIGS. 3 and 4, and since distance 336 isless than distance 334, the amount of fluid F drawn into and expelledfrom through-bores 318 and 320 in FIG. 3 increases in comparison to theamount of fluid F drawn into through-bores 318 and 320 in FIG. 4. Thusrate 332 in FIG. 3 is greater than rate 338 in FIG. 4.

FIG. 5 is a schematic representation of variable displacement bent-axispump 400 including actuator 100 of FIG. 1 or actuator 200 of FIG. 2.Pump 400 includes: housing 402; inlet port 404, outlet port 406; shaft408 with axis of rotation AR3; cylinder block 410 with axis of rotationAR4; universal joint 411 connecting block 410 to shaft 408; swash plate412 non-rotatably connected to shaft 408; and electromechanical actuator100. The discussion that follows assumes actuator 100 is included inpump 400; however, it should be understood that the discussion foractuator 100 in pump 400 is applicable to actuator 200 in pump 400.

Block 410 includes: through-bores 418 and 420; and pistons 422 and 424engaged with swash plate 412 and at least partly disposed inthrough-bores 418 and 420, respectively. Cylinder block 410 rotates withshaft 408 and about axis AR4 due to the action of joint 411. Axis AR4 isdisplaceable in directions CD3 and CD4 with respect to axis AR3.

Swash plate 412 is arranged to displace pistons 422 and 424 withinthrough-bores 418 and 420, respectively, to draw fluid F through port404 into through-bores 418 and 420 and to expel fluid F fromthrough-bores 418 and 420 into port 406.

Swash plate 412 rotates about axis AR3 with shaft 408. Pistons 422 and424 remain engaged to plate 412 as is known in the art. Block 410rotates about axis AR4 with shaft 408 and plate 412. As cylinder block410 rotates about axis AR4: when piston 422 or 424 is aligned with port404, plate 412 displaces piston 422 or 424 in direction AD3, withinthrough-bores 418 or 420, respectively, to draw fluid F intothrough-bore 418 or 420 through port 404 (the displacement createssuction at port 404); and when piston 422 or 424 is aligned with port406, plate 412 displaces piston 422 or 424 in direction AD4, withinthrough-bores 418 or 420, respectively, to expel fluid F fromthrough-bore 418 or 420 into port 406 at a flow rate. In FIG. 5, theflow rate is flow rate 432.

Pump 400 is located in device D (for example, a bulldozer, tractor, orconstruction equipment). Shaft 408 is rotated by engine E of device D.Actuator 100 is arranged to receive, from processor P, control signal428. Actuator 100 is arranged to: pivot cylinder block 410 about axisA2, transverse to axis of rotation AR3 and AR4 according control signal428; or maintain a circumferential position of cylinder block 410, aboutaxis A2, according to control signal 428.

A flow rate at which fluid is drawn into and expelled from pump 400 isdependent upon the speed of rotation of shaft 408 and the displacementof pistons 422 and 424, by plate 412, within through-bores 418 and 420,respectively. The speed of rotation of block 410 is a function of engineE, which is determined by operations other than those for pump 400. Thatis, the speed of rotation is not controllable by pump 400. For a givenposition of block 410 about axis A2, increasing or decreasing the speedof rotation of block 410 increases or decreases flow rate 432,respectively.

A flow rate for pump 400 is also governed by the circumferentialposition of block 410 with respect to axis A2. The circumferentialposition of block 410 determines the distance that pistons 422 and 424are displaced by plate 412 within through-bores 418 and 420,respectively. In the example of FIG. 5, pistons 422 and 424 aredisplaced distance 434 by plate 412 within through-bores 418 and 420,respectively. Thus, pistons 422 and 424 displace distance 434 to drawfluid F into through-bores 418 and 420, respectively, and pistons 422and 424 displace distance 434 to expel fluid F from through-bores 418and 420, respectively.

As discussed below, changing the extent of the axial displacement ofpistons 422 and 424 (for example, distance 434) changes the amount offluid F drawn into and expelled by block 410 and hence changes flow rate432.

FIG. 6 shows variable displacement bent-axis pump 400 of FIG. 5 withblock 410 pivoted. In the example of FIG. 6, block 410 has been rotatedin direction CD4 about axis A2 from the position shown in FIG. 5. Thealignment of through-bores 418 and 420 with ports 404 and 406 remainsthe same. The rotation and subsequent tilting of swash plate 412 in FIG.6 changes the axial displacement of pistons 422 and 422 by plate 412. Asa result: pistons 422 and 424 are displaced distance 436 by plate 412.In the example of FIGS. 5 and 6: distance 436 is less than distance 434.

Assuming a constant speed of rotation of shaft 408 in FIGS. 5 and 6, andsince distance 436 is less than distance 434, the amount of fluid Fdrawn into and expelled from through-bores 418 and 120 in FIG. 6decreases in comparison to the amount of fluid F drawn intothrough-bores 418 and 420 in FIG. 5. Thus flow rate 438 in FIG. 6 isless than rate 432 in FIG. 5.

The following discussion is directed to a transition from FIG. 6 to FIG.5. To transition from FIG. 6 to FIG. 5, block 410 is pivoted about axisA2 in direction CD3. Assuming the constant speed of rotation of shaft408 in FIGS. 5 and 6, and since distance 436 is less than distance 434,the amount of fluid F drawn into and expelled from through-bores 418 and420 in FIG. 5 increases in comparison to the amount of fluid F drawninto through-bores 418 and 420 in FIG. 6. Thus rate 432 in FIG. 5 isgreater than rate 438 in FIG. 6.

The following should be viewed in light of FIGS. 1 through 6. Thefollowing describes a method of operating variable displacementhydraulic pump 300 or 400. Although the method is presented as asequence of steps for clarity, no order should be inferred from thesequence unless explicitly stated. It should be understood that themethod is applicable to pump 300 or pump 400 including actuator 100 or200 unless indicated otherwise. This conflation of applicability isshown by designating respective elements included in the method with thenomenclature “3xx/4xx.” For example, the first step cites drive shaft308/408. A first step rotates, with drive shaft 308/408, cylinder block310/410. A second step draws fluid F through inlet port 304/404 and intothrough-bore 318/418. A third step expels fluid F from through-bore318/418 and through outlet port 306/406 at flow rate 332/432. A fourthstep rotates, with electric motor 104/204, roller screw 106 or nut 208.A fifth step axially displaces actuator pin 110/210. A sixth step:pivots, with actuator pin 110/210, swash plate 312/412 about axis A1/A2and controls an amount of fluid expelled from through-bore 318/418. Inan example embodiment, a seventh step blocks, with resilient element 120in actuator 100, axial displacement of actuating pin 110.

In an example embodiment, the fourth step rotates roller screw 106 andan eighth step: rotates, with electric motor 104, roller screw 106 incircumferential direction CD1; displaces, with roller screw 106,actuator pin 110 in axial direction AD1; pivots, with actuator pin 110,swash plate 312/412 about axis A1/A2 in circumferential direction CD3;generates flow rate 338/438; rotates, with electric motor 104, rollerscrew 106 in circumferential direction CD2; displaces, with roller screw106, actuator pin 110 in axial direction AD2; pivots, with actuator pin110, swash plate 312/412 about axis A1 in circumferential direction CD4;and generates flow rate 332/432.

In an example embodiment, the fourth step rotates nut 208 and an eighthstep: rotates, with electric motor 204, nut 208 in circumferentialdirection CD1; displaces, with roller screw 206, actuator pin 210 inaxial direction AD1; pivots, with actuator pin 210, swash plate 312/412about axis A1/A2 in circumferential direction CD3; generates flow rate338/438; rotates, with electric motor 104, nut 208 in circumferentialdirection CD2; displaces, with roller screw 206, actuator pin 210 inaxial direction AD2; pivots, with actuator pin 210, swash plate 312/412about axis A1 in circumferential direction CD4; and generates flow rate332/432.

It will be appreciated that various of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. Variouspresently unforeseen or unanticipated alternatives, modifications,variations, or improvements therein may be subsequently made by thoseskilled in the art which are also intended to be encompassed by thefollowing claims.

LIST OF REFERENCE CHARACTERS

-   A1 axis transverse to axis AR1 and AR2-   A2 axis transverse to axis AR1 and AR2-   AD1 axial direction-   AD2 axial direction-   AR1 axis of rotation for nut 108-   AR2 axis of rotation for roller screw 206-   AR3 axis of rotation for shafts 308 and 408-   AR4 axis of rotation for cylinder blocks 310 and 410-   CD1 circumferential direction about axis AR1-   CD2 circumferential direction about axis AR1-   CD3 circumferential direction about axis A1 and A2-   CD4 circumferential direction about axis A1 and A2-   100 axial pump-   102 housing-   104 electric motor-   106 roller screw-   108 nut-   110 actuator pin-   112 stator-   114 rotor-   116 threads-   118 threads-   120 resilient element-   200 axial pump-   202 housing-   204 electric motor-   206 roller screw-   208 nut-   210 actuator pin-   212 stator-   214 rotor-   216 threads-   218 threads-   220 resilient element-   300 axial pump-   302 housing-   304 port-   306 port-   308 shaft-   310 cylinder block-   312 swash plate-   318 through-bore-   320 through-bore-   322 piston-   324 piston-   330 retention assembly-   332 flow rate-   334 axial displacement distance-   336 axial displacement distance-   338 flow rate-   400 axial pump-   402 housing-   404 port-   406 port-   408 shaft-   410 cylinder block-   412 swash plate-   418 through-bore-   420 through-bore-   422 piston-   424 piston-   430 retention assembly-   432 flow rate-   434 axial displacement distance-   436 axial displacement distance-   438 flow rate

1. A variable displacement hydraulic pump, comprising: an inlet port; anoutlet port; a cylinder block including a first piston disposed in afirst through-bore; a swash plate engaged with the first piston; a driveshaft: non-rotatably connected to the cylinder block; arranged to rotatethe cylinder block to draw fluid through the inlet port into the firstthrough-bore and to expel the fluid from the first through-bore andthrough the outlet port; and, including an axis of rotation; an axistransverse to the axis of rotation; and, an actuator including: a rollerscrew; a nut disposed about the roller screw and in threaded contactwith the roller screw; an actuator pin engaged with the roller screw;and, an electric motor arranged to rotate the roller screw or the nut toaxially displace the actuator pin to: pivot the swash plate about theaxis and control an amount of the fluid expelled from the firstthrough-bore; or, pivot the cylinder block about the axis and control anamount of the fluid expelled from the first through-bore.
 2. Thevariable displacement hydraulic pump of claim 1, wherein the actuatorincludes a resilient element urging the roller screw in a first axialdirection.
 3. The variable displacement hydraulic pump of claim 1,wherein: the electric motor is arranged to rotate the roller screw orthe nut to axially displace the actuator pin to pivot the swash plateabout the axis; the cylinder block includes: a second through-bore; and,a second piston disposed in the second through-bore and engaged with theswash plate; and, rotation of the cylinder block is arranged to:displace the first piston within the first through-bore; displace thesecond piston within the second through-bore; draw the fluid through theinlet port into the second through-bore; and, expel the fluid from thesecond through-bore and through the outlet port.
 4. The variabledisplacement hydraulic pump of claim 1, wherein: the electric motor isarranged to rotate the roller screw or the nut to pivot the cylinderblock about the axis; the cylinder block includes: a secondthrough-bore; and, a second piston disposed in the second through-boreand engaged with the swash plate; and, rotation of the cylinder block isarranged to: displace the first piston within the first through-bore;displace the second piston within the second through-bore; draw thefluid through the inlet port into the second through-bore; and, expelthe fluid from the second through-bore and through the outlet port. 5.The variable displacement hydraulic pump of claim 1, wherein: theelectric motor is arranged to rotate the roller screw to axiallydisplace the actuator pin to pivot the swash plate about the axis; theelectric motor is arranged to rotate the roller screw in a firstcircumferential direction about the axis of rotation to displace theactuator pin in a first axial direction; the actuator pin is arranged topivot the swash plate about the axis in a second circumferentialdirection to increase the amount of fluid expelled from the firstthrough-bore; the electric motor is arranged to rotate the roller screwin a third circumferential direction, opposite the first circumferentialdirection, about the axis of rotation to displace the actuator pin in asecond axial direction, opposite the first axial direction; and, theactuator pin is arranged to pivot the swash plate about the axis in afourth circumferential direction, opposite the second circumferentialdirection to decrease the amount of fluid expelled from the firstthrough-bore.
 6. The variable displacement hydraulic pump of claim 1,wherein: the electric motor is arranged to rotate the nut to axiallydisplace the actuator pin to pivot the swash plate about the axis; theelectric motor is arranged to rotate the nut in a first circumferentialdirection about the axis of rotation to displace the actuator pin in afirst axial direction; the actuator pin is arranged to pivot the swashplate about the axis in a second circumferential direction to increasethe amount of fluid expelled from the first through-bore; the electricmotor is arranged to rotate the nut in a third circumferentialdirection, opposite the first circumferential direction, about the axisof rotation to displace the actuator pin in a second axial direction,opposite the first axial direction; and, the actuator pin is arranged topivot the swash plate about the axis in a fourth circumferentialdirection, opposite the second circumferential direction to decrease theamount of fluid expelled from the first through-bore.
 7. The variabledisplacement hydraulic pump of claim 1, wherein: the electric motor isarranged to rotate the roller screw to axially displace the actuator pinto pivot the cylinder block about the axis; the electric motor isarranged to rotate the roller screw in a first circumferential directionabout the axis of rotation to displace the actuator pin in a first axialdirection; the actuator pin is arranged to pivot the cylinder blockabout the axis in a second circumferential direction to increase theamount of fluid expelled from the first through-bore; the electric motoris arranged to rotate the roller screw in a third circumferentialdirection, opposite the first circumferential direction, about the axisof rotation to displace the actuator pin in a second axial direction,opposite the first axial direction; and, the actuator pin is arranged topivot the swash plate about the axis in a fourth circumferentialdirection, opposite the second circumferential direction to decrease theamount of fluid expelled from the first through-bore.
 8. The variabledisplacement hydraulic pump of claim 1, wherein: the electric motor isarranged to rotate the nut to axially displace the actuator pin to pivotthe cylinder block about the axis; the electric motor is arranged torotate the nut in a first circumferential direction about the axis ofrotation to displace the actuator pin in a first axial direction; theactuator pin is arranged to pivot the cylinder block about the axis in asecond circumferential direction to increase the amount of fluidexpelled from the first through-bore; the electric motor is arranged torotate the nut in a third circumferential direction, opposite the firstcircumferential direction, about the axis of rotation to displace theactuator pin in a second axial direction, opposite the first axialdirection; and, the actuator pin is arranged to pivot the cylinder blockabout the axis in a fourth circumferential direction, opposite thesecond circumferential direction to decrease the amount of fluidexpelled from the first through-bore.
 9. The variable displacementhydraulic pump of claim 1, wherein: the actuator pin is arranged topivot the swash plate about the axis; and, the actuator pin is arrangedto pivot the swash plate about the axis to control an extent ofdisplacement of the first piston within the first through-bore.
 10. Thevariable displacement hydraulic pump of claim 1, wherein: the actuatorpin is arranged to pivot the cylinder block about the axis; and, theactuator pin is arranged to pivot the cylinder block about the axis tocontrol an extent of displacement of the first piston within the firstthrough-bore.
 11. A variable displacement hydraulic pump, comprising: aninlet port; an outlet port; a cylinder block including: a through-bore;and, a piston at least partially disposed in the through-bore; a driveshaft: non-rotatably connected to the cylinder block; arranged to rotatethe cylinder block to displace the piston to draw fluid through theinlet port into the through-bore and expel the fluid from thethrough-bore and through the outlet port; and, including an axis ofrotation; an axis transverse to the axis of rotation; an actuatorincluding: a roller screw; a nut disposed about and in contact with theroller screw; an actuator pin engaged with the roller screw and theswash plate; and, an electric motor arranged to rotate the roller screwto axially displace the actuator pin to: pivot the swash plate about theaxis and control an amount of the fluid expelled from the through-bore;or, pivot the cylinder block about the axis and control an amount of thefluid expelled from the through-bore.
 12. A variable displacementhydraulic pump, comprising: an inlet port; an outlet port; a cylinderblock including: a through-bore; and, a piston at least partiallydisposed in the through-bore; a drive shaft: non-rotatably connected tothe drive shaft; arranged to rotate the cylinder block to displace thepiston to draw fluid through the inlet port into the through-bore andexpel the fluid from the through-bore and through the outlet port; and,including an axis of rotation; an axis transverse to the axis ofrotation; an actuator including: a roller screw; a nut disposed aboutand in contact with the roller screw; an actuator pin engaged with theroller screw and the swash plate; and, an electric motor arranged torotate the nut to axially displace the actuator pin to: pivot the swashplate about the axis and control an amount of the fluid expelled fromthe through-bore; or, pivot the cylinder block about the axis andcontrol an amount of the fluid expelled from the through-bore.
 13. Amethod of operating the variable displacement hydraulic pump of claim 1,comprising: rotating, with the drive shaft, the cylinder block; drawingthe fluid through the inlet port and into the first through-bore;expelling the fluid from the first through-bore and through the outletport; rotating, with the electric motor, the roller screw or the nut;axially displacing the actuator pin; and, pivoting, with the actuatorpin: the swash plate about the axis and controlling an amount of thefluid expelled from the first through-bore; or, the cylinder block aboutthe axis and controlling an amount of the fluid expelled from the firstthrough-bore.
 14. The method of claim 13, further comprising: blocking,with a resilient element in the actuator, axial displacement of theactuating pin.
 15. The method of claim 13, further comprising: pivoting,with the actuator pin, the swash plate about the axis; rotating, withthe electric motor, the roller screw in a first circumferentialdirection about the axis of rotation; displacing, with the roller screw,the actuator pin in a first axial direction; pivoting, with the actuatorpin, the swash plate about the axis in a second circumferentialdirection; increasing the amount of fluid expelled from the firstthrough-bore; rotating, with the electric motor, the roller screw in athird circumferential direction, opposite the first circumferentialdirection, about the axis of rotation; displacing, with the rollerscrew, the actuator pin in a second axial direction, opposite the firstaxial direction; pivoting, with the actuator pin, the swash plate aboutthe axis in a fourth circumferential direction, opposite the secondcircumferential direction; and, decreasing the amount of fluid expelledfrom the first through-bore.
 16. The method of claim 13, furthercomprising: pivoting, with the actuator pin, the cylinder block aboutthe axis; rotating, with the electric motor, the roller screw in a firstcircumferential direction about the axis of rotation; displacing, withthe roller screw, the actuator pin in a first axial direction; pivoting,with the actuator pin, the cylinder block about the axis in a secondcircumferential direction; increasing the amount of fluid expelled fromthe first through-bore; rotating, with the electric motor, the rollerscrew in a third circumferential direction, opposite the firstcircumferential direction, about the axis of rotation; displacing, withthe roller screw, the actuator pin in a second axial direction, oppositethe first axial direction; pivoting, with the actuator pin, the cylinderblock about the axis in a fourth circumferential direction, opposite thesecond circumferential direction; and, decreasing the amount of fluidexpelled from the first through-bore.
 17. The method of claim 13,further comprising: pivoting, with the actuator pin, the swash plateabout the axis; rotating, with the electric motor, the nut in a firstcircumferential direction about the axis of rotation; displacing, withthe roller screw, the actuator pin in a first axial direction; pivoting,with the actuator pin, the swash plate about the axis in a secondcircumferential direction; increasing the amount of fluid expelled fromthe first through-bore; rotating, with the electric motor, the nut in athird circumferential direction, opposite the first circumferentialdirection, about the axis of rotation; displacing, with the rollerscrew, the actuator pin in a second axial direction, opposite the firstaxial direction; pivoting, with the actuator pin, the swash plate aboutthe axis in a fourth circumferential direction, opposite the secondcircumferential direction; and, decreasing the amount of fluid expelledfrom the first through-bore.
 18. The method of claim 13, furthercomprising: pivoting, with the actuator pin, the cylinder block aboutthe axis; rotating, with the electric motor, the nut in a firstcircumferential direction about the axis of rotation; displacing, withthe roller screw, the actuator pin in a first axial direction; pivoting,with the actuator pin, the cylinder block about the axis in a secondcircumferential direction; increasing the amount of fluid expelled fromthe first through-bore; rotating, with the electric motor, the nut in athird circumferential direction, opposite the first circumferentialdirection, about the axis of rotation; displacing, with the rollerscrew, the actuator pin in a second axial direction, opposite the firstaxial direction; pivoting, with the actuator pin, the cylinder blockabout the axis in a fourth circumferential direction, opposite thesecond circumferential direction; and, decreasing the amount of fluidexpelled from the first through-bore.
 19. The method of claim 13,further comprising: pivoting, with the actuator pin, the swash plateabout the axis; and, controlling, with the swash plate, an extent ofdisplacement of the first piston within the first through-bore.
 20. Themethod of claim 12, further comprising: pivoting, with the actuator pin,the cylinder block about the axis; and, controlling, with the swashplate, an extent of displacement of the first piston within the firstthrough-bore.